1. Technical Field
This invention relates generally to dynamoelectric machines and more specifically to a stator assembly for inductor type rotating dynamoelectric machines capable of operating over a wide speed range, including high speeds.
2. Background Art
Adjustable speed drives conventionally employ general purpose motors that are selected from standard designs based on such characteristics as low reactance, the ability to operate over a given speed range, and heat rejection capability at the anticipated operating speeds. This approach results in usable designs, but also notable limitations, particularly in speed capability and overall system performance.
For high speed applications, dynamoelectric machines of various known constructions have been tried but with limited success. Synchronous and induction type motors, for example, are mechanically limited at high speeds due to the lack of physical integrity of the rotating structure (which includes the shaft, pole pieces and field winding) at high rotational speeds. This has resulted in few applications of the induction type machine above 3600 rpm. Gears can, of course, be used to multiply the output speed of the standard induction motor but this has not proven particularly reliable at higher multiplication factors. Further, there are limits with respect to how much one can "gear up".
In other high speed applications, a small, "universal" type motor or a permanent magnet motor have been employed. However, the universal type motor is not especially efficient and is difficult to scale up. The permanent magnet motor, on the other hand, is not very cost effective and is also impractical for large machines. Variable-reluctance type machines (with no field winding), have recently been proposed for certain applications, but generally use laminated rotors which tend to come apart at high speeds.
Another attempt to realize high speed operation, particularly for electrical generation, employs an inductor type dynamoelectric machine. Such machines are generally characterized by a stator which includes both AC armature and DC excitation coils, surrounding a coil-less rotor. Since there are no rotating field or armature coils in this type of dynamoelectric machine, slip rings, brushes and associated connections, common to machines having rotating windings, may be entirely eliminated. This feature, coupled with the typical solid construction of the machine rotor, makes the inductor machine particularly adaptable to high rotational speed applications.
One known version of an inductor type rotating dynamoelectric machine, employs a circumferentially distributed arrangement of "C" or "U" shaped armature elements surrounding a generally cylindrical field coil which in turn encloses a transverse pole magnetic rotor. U.S. Pat. No. 437,501 to W. M. Mordey, for example, describes an "Electric Generator" having a stator assembly which employs a stationary cylindrical field coil, and "U" shaped magnetic pieces alternately disposed and oppositely directed on opposite sides of a single armature coil. In the Mordey arrangement, the U-shaped magnetic pieces and single armature coil are carried by bolted together side frames. The field winding is held stationary by straps encircling the winding; the ends of the straps are attached to longitudinal rods extending between the side frames (reference FIG. 3 of the Mordey patent and the description thereof).
U.S. Pat. No. 2,519,097 to F. J. Allen describes an inductor type dynamoelectrical machine which also employs a circumferentially distributed arrangement of arch or U-shaped armature elements enclosing a stationary field winding and a rotatable transverse pole rotor. As in the Mordey patent, the armature elements of Allen are mounted to an external frame. A more recent version of this dynamoelectric machine configuration, is illustrated in U.S. Pat. No. 3,912,958 for a "Flux-Switched Inductor Alternator" issued to D. B. Steen. Although the details of mounting the stator assembly are not fully depicted or described in the Steen patent, in one embodiment (i.e. FIG. 3) the plurality of circumferentially distributed stator bars are mechanically connected to a thermomagnetic flux ring at one end of the stator assembly which serves to support the bars.
Although the above described prior implementations of inductor type machines are capable of high speed operation, they suffer from certan practical limitations. Each appears to be directed primarily at electrical generation. It would, of course, be desirable to configure such a machine so that it is suitable for operation in all four quadrants, i.e. generation, motoring, forward and reverse. Further, to optimize machine operation, it is highly desirable to be able to readily precisely position the various armature elements, axially, radially and circumferentially, and to maintain said precise positioning and associated critical inter-component spacing during machine operation. The external mounting arrangements of the prior art do not effectively achieve this objective and also complicate the assembly, disassembly and repair of the machine. Further refinements in cooling such machines during operation and in providing enhanced flux shielding are also desirable.